Intracellular expression of Fas Ligand and Granzyme B by tumor infiltrating or in vitro activated CD8+ T cell populations

• Author / Creator

  Scott, Amanda N.

• CD8+ T cells can recognize infected or cancerous cells and eliminate them by exocytosing cytolytic molecules or presenting death ligands on their surface, both of which can initiate apoptosis in target cells. Granzyme B (GzmB) and Fas Ligand (FasL) are two of the effector proteins that CD8+ T cells can use to kill infected or cancerous cells. GzmB is a soluble protein that shares a vesicle with other cytolytic enzymes that enter the target cell upon degranulation, and FasL is a transmembrane ligand that can engage with the Fas death receptor on target cells. Past research has shown that these two cytolytic proteins can be stored and trafficked within the cell differently, and can be presented to the target cell in response to different T cell receptor signal strength in the context of target cell recognition. Furthermore, there is debate as to whether FasL is required for, contributes to, or is dispensable for clearance of tumors. Most of these studies have not characterized whether FasL protein is actually present in the cells responding to the tumors, or whether extrinsic factors can influence FasL protein expression in CD8+ T cells. As CD8+ T cells have the potential to be exploited therapeutically for patients with cancer, it is important to better understand expression patterns of effector mechanisms in activated CD8+ T cells and how these can be manipulated.I used two approaches to examine the relationship between FasL and GzmB expression in CD8+ T cells and the environment these cells are in. First, I activated naïve CD8+ T cells under controlled conditions in vitro and characterized FasL and GzmB protein expression dynamics after changes to the cytokine milieu. Second, I injected mice with subcutaneous or intraperitoneal EG.7 lymphoma and analyzed the CD8+ T celliiiresponse in secondary lymphoid tissue and in the tumor sites. I found that overall, multiple CD8+ subsets can intracellularly express FasL, either coexpressed with GzmB or in the absence of GzmB. FasL expression in CD8+ T cells is influenced by the in vitro activation and in vivo tumor environment in ways unique from GzmB, with some conditions that are unfavorable for GzmB expression eliciting intracellular FasL expression. Furthermore, FasL protein expression in tumor-responding CD8+ T cells is not influenced by T cell reactivity to the immunodominant tumor antigen, unlike GzmB. Both memory and effector CD8+ T cells can express intracellular FasL and/or intracellular GzmB, though FasL/GzmB coexpression is more likely to be associated with an effector or recently activated PD-1hi phenotype. Overall, these findings shed light on the independent expression of FasL and GzmB by CD8+ T cells and the ubiquity of intracellular FasL expression in activated CD8+ T cell subtypes.

• Subjects / Keywords

  • tumor infiltrating cells
  • Fas Ligand
  • CD8+ T cell
  • tumour infiltrating cells

• Graduation date

  Spring 2019

• Type of Item

  Thesis

• Degree

  Doctor of Philosophy

• DOI

  https://doi.org/10.7939/r3-j47p-0v68

• License

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